An insecure or corrupt government will never let dissent go without punishment. If you are organizing a protest against such a government you must be prepared for consequences.
The protest can be a peaceful sit in, a march to a significant place or even a violent measure (although this should not be a consideration). Whatever happens, you can expect an aggressive reply from the government. If this happens you should know what to expect and what to do about it.
Water cannons are a big favorite to disperse crowds. The force from these cannons is quite devastating and can knock a person of their feet. At this point they can be slammed against other hard objects and be injured. Make sure you have medical personnel on standby to help them or to take them to a hospital.
Tear gas is another method of crowd dispersal and quite an effective one. To counter this you need motorcycle helmets or some sort of face protector. If everyone is unable to bring one, tell them to bring plenty of water and a spare towel or t-shirt. Soak the cloth in water and wrap it around your head to avoid breathing in the fumes.
To counter any human rights violations, place several people with video cameras and digital cameras in strategic locations. Get them to record everything that goes in the protest when the crackdown starts. This way, any dirty tactics that were used can be highlighted and contested in a court of law.